Spatial Audio Processing: MPEG Surround and Other Applications

Preface

The physical and practical limitations that have to be considered in the field of audio engineering include limited directionality of microphones, limited number of audio channels, the need for backwards compatibility, storage and transmission channel constraints, loudspeaker positioning, and cost, which may dictate other restrictions.

There is a long history of interaction between the fields of audio engineering and psychoacoustics. In many cases, the reason for this interaction is to achieve a certain goal given the imposed limitations. For example, in the 1970s the first widely used cinema surround systems applied psychoacoustic knowledge to improve their perceptual performance. Specifically, due to technical limitations the method of representing multi-channel audio often caused a lot of crosstalk between various loudspeaker signals, resulting in a risk that the front dialogue was occasionally perceived from behind. To prevent this, delays were applied motivated by the psychoacoustic ‘law of the first wavefront’ (sound is often perceived from the direction from which the ‘first wavefront’ arrives and delayed reflections arriving from different directions are not perceived explicitly). Another example is that the spectral content of the center dialogue loudspeaker in cinemas is modified such that the dialogue is perceived from above the center loudspeaker, i.e. from the center of the screen as is desired.

A more recent example of how psychoacoustic knowledge benefits ...